Splice case for optical fibre cable

ABSTRACT

An enclosure capable of enclosing a butt splice between at least two optical fibre cables, which comprises: a base through which respective cables can pass; at least one optical fire organizer capable of storing an optical fibre in the path from one of the outlets to another of the outlets, said path having a minimum radius of curvature no smaller than the minimum bend radius of said optical fibre; and a hollow cover which can surround the organizer and which can be fixed to the base to close the enclosure; the base being removable from the splice by sliding over the organizer.

The present invention relates to the provision of an environmental sealaround a splice in one or more optical fibre cables.

Optical fibre cables comprise a bundle of optical fibres surrounded by aprotective jacket. Since such cables are manufactured in finite lengths,any installation will in general require separate lengths of cable to bespliced together. A problem arises at the splice, not only in formingfibre splices of low light attenuation, but also in replacing theprotective jacket which has to be removed in the region of the splice toexpose the fibres. It is with this second problem that the presentinvention is concerned,

Splicing an optical fibre is a difficult business, requiring use of amachine for proper alignment of pairs of fibres before a permanentsplice is made between each pair. The machine will of necessity be someshort distance away from the ends of the intact portions of the cablesto be joined, i.e. some distance from the ends of each cable jacket. Thejacket of each cable to be joined may be stripped back a distance of,say, 1.5 m thereby exposing 1.5 m of optical fibres. It can be seen,therefore, that there is a further problem, namely the accomodation of asignificant length of optical fibres within the environmental housingwhich is to replace the removed portions of cable jacket. Optical fibresare easily broken by being bent around too sharp a radius, and thehousing must therefore provide some way of organizing the fibres alongan acceptable path.

There are some further considerations. It will generally be desirablethat any chosen fibre within the housing is accessible, and thereforethe fibres, which may number hundreds, should be organized within thehousing in a regular fashion. Also, some means of identifying each fibreis desirable, and such means may have to be by way of its locationwithin the housing since colour coding of the fibre itself is difficult.

Various suggestions have been proposed for an optical fibre splice casewhich organizes the slack lengths of fibres and provides anenvironmentally sealed housing around them.

In European patent publication 0043570 there is proposed an opticalfibre splice case through one side of which one cable enters and throughan opposite side of which another cable enters. The ingoing cables aresealed to inlets of the case by shrinkable sleeves. Within the case is aseries of plates, each with projections thereon around which are woundthe spliced fibres, thereby storing the slack lengths in a path whichdoes not result in damage to the fibres. Such a splice case is known asan in-line splice case (as opposed to a butt splice case) since thecables enter the case from opposite ends, or at least from widely spacedpositions.

A similar series of plates for use in an in-line cable splice isdisclosed in U.S. Pat. No. 4,266,853. Here the plates are stacked one ontop of another and are hinged to a carrier. The hinging allows a chosenplate to be revealed for attention to a fibre splice it carries.

Optical fibre cables may be, for example, buried, or aerial, suspendedbetween poles. In each case in addition to providing environmentalprotection, some mechanical strength has to be provided, and particularattention has to be given to axial pull strength in the case of aerialinstallations. Many of the prior art designs provide for axial pullstrength in the following way. The cables themselves may be providedwith a steel wire core, around which the fibres are located. In additionto preventing excessive bending of the cable, the core can be used totransmit axial load through the splice case, thus eliminating axial loadon the fibres themselves. The way this is done is to strip back thejacket of each cable in the usual way to expose sufficient lengths offibres for the splicing process to be carried out. The metal core of onecable is then clamped to one end of the splice case and the core of theother cable is clamped to the opposite end of the splice case. Thus, anyaxial load is transmitted from one core in a line through the case tothe other core. Such an arrangement is disclosed in European PatentPublication No. 0077115.

Various other designs for optical fibre splice cases are disclosed in DE3006131, JP-A-55-127508, JP-A-55-127507, JP-A-55-100504 andJP-A-52-133146.

Although most of the designs proposed in the prior art are likely to besatisfactory each has a disadvantage. The splice cases tend to be bulky,difficult to remove from a manhole or pole where they are located, anddifficult to re-enter for repair or testing. We have discovered thatthese problems can be overcome by a simple modification to thearrangement of the cables and organizer plates.

The invention in EP0159857 (Raychem) provides an enclosure capable ofenclosing a butt splice between at least two optical fibre cables, whichcomprises:

a base having at least two mutually adjacent outlets capable ofreceiving respective cables;

at least one optical fibre organizer attachable to the base and capableof storing a plurality of optical fibres, each of said fibres describinga path from one of the outlets to another of the outlets, said pathhaving a minimum radius of curvature no smaller than the minimum bendradius of said optical fibre; and

a hollow cover which can surround the organizer and which can be fixedto the base to close the enclosure, preferably by sliding over theorganizer axially with respect to the cables entering the base.

An enclosure of this design can be made easy to re-enter because an end(i.e. the cover), rather than a middle portion, of the assembly can beremoved. This is because the cables to be spliced enter the assemblyfrom one end. The assembly can be of substantially tubular design ofsmall diameter and length, the design of the internal organizer can besimplified, and a temporary seal (e.g. over night during a lengthyinstallation) around the organizer can be made using the cover ratherthan a wrap-around sheet. Furthermore, the assembly can be easilyremoved from a man-hole or pole. This is because sufficient free cablewill be available due to one of the ingoing cables having been bent in acurve in order to enter the assembly. (Imagine two horizontal cables tobe spliced; one enters the assembly directly, and the other will curvethrough a semi-circle to enter the same end of the assembly.) If anin-line cable splice is used, there is either no cable slack at all andthe splice cannot be moved; or the cable needs to curve at both endsrequiring a larger man-hole or more extensive cable pole fixings.

The base preferably comprises a plate having two or more outlets, eitheras simple apertures or as tubular projections, and the cover preferablyis generally cylindrical with one closed end, for example dome-shaped.The base plate mates with the open end of the dome to provide the hollowarticle. Some means of holding the two parts together will preferably beprovided, although the two parts may simply be an interference fit.Examples of means for holding them together include screw-threads on thetwo parts, bayonet fixings on the two parts, catches on the two parts, aseparate clamp, and a separate sealing band for example aheat-shrinkable or otherwise recoverable band. Mechanical holding of thetwo parts may be combined with some environmental sealing means such asa gasket, O-ring, mastic seal or adhesive bond. An adhesive bond couldbe used in the absence of any mechanical fixing.

The base is preferably so constructed to allow core blocking of thecables that pass through it. This may be done by providing a reservoiror means for constructing a reservoir into which an encapsulant can bepored or pumped. A portion of each cable stripped of its outer jacketpasses through the reservoir such that introduction of an encapsulant,which may cure or otherwise solidify, provides core blocking or furtherseals the cable outlet, or screens the spliced fibres from any metalwork present.

The outlets are preferably in the form of tubes protruding from the base(or other part) of the hollow article, and means is preferably providedfor environmentally sealing the outlets to the cables that pass throughthem. For example, a clamp, such as a hose clamp, could be used aroundthe tubular outlets. A second possibility is to provide an adhesive, amastic, or other sealing material between the cables and the outlets. Weprefer, however, that the outlets be heat-shrinkable or otherwiserecoverable since a tight seal can thus be made between any given outletand a wide variety of sizes of cables. Heat-recoverability may of coursebe used in conjunction with a sealing material such as aheat-activatable adhesive.

In general, the two or more outlets may be provided in two basic ways.Firstly they may be independent in the sense that the base (or otherpart) of the hollow article is moulded or otherwise formed with tubularoutlets projecting therefrom at two or more separate positions. In asecond technique one (or more) large outlet is provided on the hollowarticle, which is subsequently divided into the requisite number ofsmaller outlets; or, what may amount to the same thing, means isprovided to obviate the re-entrant gaps that would otherwise provideleak paths between the two or more cables and the large conduit thatcarries them. This may be done either by providing a flexible sealaround the two or more cables to change their combined re-entrantcross-sectional shape into a generally circular shape compatible withthat of the outlet, or by using a branch-off clip (such as thatdisclosed in GB 1604981 or 1604985) to deform the outlet to match thecross-sectional shape of the cables. (These techniques are illustratedin the drawings.)

Whether or not independent conduits or a divided large conduit is used,a seal is preferably made or enhanced by the conduits or conduit beingrecovered into engagement with the cable or cables. Recovery ispreferably brought about by heat. Heat may be supplied by a torch or ahot-air gun although neither of them can supply heat sufficientlylocally to recover easily one only of several independant conduits. Weprefer therefore to provide self-contained heating means, and theinvention thus also provides an optical fibre splice case comprising: ahollow article having recoverable cable outlets with self containedheating means; and an optical fibre organizer.

The self-contained heating means preferably comprises an electricalheating means such as a resistive heating wire or a conductive polymercomposition. We prefer that the electrical heating means isself-regulating with respect to temperature, and this may be achieved byusing as the heater a polymeric composition loaded with a filler such ascarbon to give a positive temperature coefficient of resistance. Theheater may be a discrete heater in thermal contact with the recoverableoutlets, or it may be integral with the outlets. Additionally oralternatively, the heater may have the function of activating aheat-activatable sealing material such as a hot-melt adhesive forfurther environmental sealing or engagement.

A preferred design of the optical fibre organizer will now beconsidered. The organizer preferably comprises one or more trays on eachof which may be stored a length of one or more optical fibres. Forexample, an organizer may have 5 to 10, preferably about 8 to 10, trays,and each tray may store 5-24, preferably about 10 or 12, optical fibres.An optical fibre cable enters the assembly through one outlet,intermediate lengths of the fibers it contains are stored on the trays,and the cable leaves the assembly through another of the outlets. Sincethe primary function of the assembly is to house a cable splice, eachtray will also hold the fibre splices themselves. A fiber splice may bemade in a small transparent tube into each end of which is inserted oneof the two fibres to be spliced. The tube contains a curablecomposition, which is caused to set once the fibres have been correctlyaligned therein. The trays may be provided with means such as recessesor clips to hold these fibre splice tubes. The assembly of the inventionmay also be used to house an intermediate section of a cable, where thejacket has been removed for testing or access, and where no fibresplices are present.

The trays are preferably stacked one on top of another and attached inthat configuration to a carrier which may be attached to or integralwith the base or other part of the enclosure. The attachment should besuch that any chosen tray may be removed or exposed in order to attendto an optical fibre it carries.

We prefer that the trays are rectangular and are attached by means of ashort side to a base of the enclosure. The trays may be hinged in orderthat they can be rotated away from the splice closure axis. Inparticular they may be hinged along an edge, preferably a short edge, soas to be moveable to expose an underlying tray. The trays then extendlengthways away from the base and are covered by the cover. The traysshould be made as small as possble consistent with the fibres they carryfollowing a path having a minimum radius of curvature equal to theminimum bend radius of the fibres in question. Preferably the path is nosmaller than the permanent bend radius of the fibres. The length of eachtray will depend on the length of each fibre that is required for thesplicing operation to be carried out and this will depend on thesplicing technique. Also each fibre may be wound around its path on theorganizer two, three or more times, thus increasing storage by factor oftwo, three or more. The extent to which this can be done will depend onthe number of fibers to be stored on each tray and on the number oftrays compared to the desired size of the assembly.

The path that each fibre follows on each tray is not critical, but forbest use of space it will pass as close to each long edge as possible. Apreferred path will therefore be oval, or rectangular with rounded shortedges. Small pegs or other protrusions may be provided on each trayaround which the fibres may be wound. The trays preferably have raisededges or rims to maintain a certain separation between them and toprevent fibre spillage from their edges. Each fibre preferably enters atray along one long edge and leaves that tray from the opposite longedge. This arrangement allows shorter trays and better fibreorganization than an alternative where the fibres enter and leave alongthe same long edge. In the case of a cable splice, the fibres will ingeneral enter and leave each tray across the same short edge. Anadvantage of them entering across the same edge is that a space wherethe fibre bundles diverge from each cable to the various trays is onlyrequired at one end of the set of trays. Thus the splice case isshorter. If they entered across opposite short edges not only would thesplice case be longer, it would also be of greater diameter due to theneed for the fibre bundles to bend within the case and pass back downthe case to pass through the outlets due to the overall butt-nature ofthe splice. This can only be avoided using an in-line splice.

The difficulty of making a splice between two optical fibres, and theneed for a special splicing device were mentioned above. The entireoperation of locating the cables to be joined, performing a large numberof splices, storing the spliced fibres, and then environmentally sealingthe resulting splices is quite complex. We have developed an apparatusfor simplifying this procedure in the field, which locates in thepreferred relationship all of the articles required.

The present invention provides a butt splice enclosure that is removablefrom the splice, without severing the spliced conductors. This may beachieved, in general, by providing components of the closure of thecorrect size relative to one another (and relative to the splice itself)that they can be slid past one another and longitudinally off the end ofthe splice. Alternatively, or additionally, one or more of thecomponents may be of so-called "wraparound" design, i.e. have a splitperiphery and can therefore be removed from the splice laterally withrespect to the cables. Since such a split periphery is likely to resultin a leak path into the closure, any components with a split peripheryare preferably provided within a tubular (i.e. non-split) component thatcan be removed by longitudinal sliding of the end of the splice.

In one embodiment, the invention provides an enclosure capable ofenclosing a butt splice between at least two optical fibre cables, whichcomprises:

a base through which respective cables can pass:

at least one optical fibre organizer capable of storing an optical fibrein a path from one of the outlets to another of the outlets, said pathhaving a minimum radius of curvature no smaller than the minimum bendradius of said optical fibre; and

a hollow cover which can surround the organizer and which can be fixedto the base to close the enclosure; the base being removably from thesplice by sliding over the organizer.

The invention is further illustrated with reference to the accompanyingdrawings, in which:

FIG. 1 shows a partially dismantled prior art butt splice case of theinvention;

FIGS. 2(a) and (b) shows bases for a prior art optical fibre splicecase;

FIG. 3 shows electrical connections to the base of FIG. 2;

FIG. 4 shows a part of a prior art base for holding trays;

FIG. 5 shows a prior art butt splice case employing branch-off clips anda junction box;

FIG. 6 shows a butt splice case employing branch-off clips;

FIG. 7 shows the use of a prior art flexible seal in a butt splice case;

FIGS. 8(a) and (b) shows construction of prior art electricallyrecoverable outlets;

FIGS. 9(a) and (b) illustrates fibre arrangements on prior art trays ofan optical fibre organizer;

FIGS. 10(a) and (b) shows a prior art tray;

FIGS. 11(a) and (b) shows a prior art splice holder; and

FIGS. 12-14 show enclosures of the invention.

FIG. 1 shows a base plate 1 and a dome-shaped cover 2 which togetherform an enclosure for use as a butt splice case for optical fibrecables. The base 1 is preferably manufactured by moulding from aglass-fibre filled high density polyethylene. Outlets 3 are provided inthe base through which the cables pass. On a new installation, some onlyof the outlets 3 may be required, and some may therefore be temporarilyblocked as shown at 4. Such blocking may be by any suitable means, butwe prefer that the outlets be made with closed ends which are simply cutoff as required. The dome-shaped cover may be blow-moulded andincorporate a moisture-vapour barrier such as a metal foil.

The hollow article contains an optical fibre organizer which comprises aseries of trays 5. Each tray preferably includes means 6 foraccomodating splice tubes which house the fibre splices. The trays arepreferably held in an orderly fashion on a carrier 7 which is fixed tothe base 1. The trays are shown hinged along their short edges, butother hinging for example pivoting for rotating e.g. about one corner inthe plane of the trays could be provided. The hinging allows chosentrays to be exposed for installation of the splices or for repair etc.Means is preferably also provided for locking the trays in their hingedposition.

The assembly of the invention may be used as follows. Firstly, pass thetwo cables to be spliced in the direction of the arrows through two ofthe outlets 3 such that, say 1.5 m of each cable protrudes into thesplice case. The cable jackets are then removed back to the base 1 toexpose 1.5 m of fibres. The strength core of each cable is then cutback, leaving enough remaining for it to be fastened into respectivefastening holes 8. Each fibre of one cable is then spliced to thecorrect fibre of the other cable. Groups of say ten or twelve splicedfibres are then stored on each tray. When one tray is filled it is movedby hinging at 9 to expose another tray. Each tray preferably has a rim10 to ensure a sufficient separation between adjacent trays and/or toprevent fibre slippage from each tray.

In FIG. 1 the outlets 3 are shown as independant tubular projections,which are preferably produced by moulding integrally with the base. Theoutlets are preferably heat-shrinkable in order that seals can be madeto the cables they carry.

The base 1 shown in FIG. 2a is novel and has some additional oralternative features to that shown in FIG. 1. This base 1 comprises amoulded or otherwise formed part 11 to which is attached a carrier 7 towhich trays may be hinged at positions 9. Cables enter the base throughoutlets 3. Provision is made for connecting (mechanically and/orelectrically) a central core of the cable and/or a cable shield or outerstrength member (for example a braid or tape wrap): the central strengthmember can be attached to connections 8 and the outer strength member(or shield) to connections 12. A connection 8 and connection 12 may beprovided for each cable.

The base is so constructed that core blocking of the cables can beprovided. A certain length of cable jacket is removed so that, when thecable is inserted through an outlet 3, the cable core is exposed over atleast part of the distance X shown in the Figure.

A reservoir may be provided by plates or other means 13 which can beattached, for example by positioning in grooves on the base. Anencapsulant may then be poured or forced into the reservoir to block thecable or to form a further seal at the cable outlet (i.e. in addition tothe sleeves 3) or to protect the interior of the splice case from anymetal work present (metal may cause liberation of hydrogen which candamage optical fibres).

A further novel variation is shown in FIG. 2b, which shows severalpartially drawn trays 5 attached to a base 1 comprising a moulded part11 and a carrier 7. In this embodiment connectors 8 for cable shieldingor for outer strength members are attached to the moulded part. This canprovide easy cable installation and easy fibre access. The dotted linesbetween connectors 8 indicate an electrically conductive strip betweenthem that can be severed for example where it is shown pleated toisolate the two connectors at the left from the two at the right.

The tray partially shown, more fully shown in FIG. 10, is of a designthat allows the tray size to be minimized. Such trays can preferablyhold splices of, say, 7.2 mm in width. Bend radii of at least 4.4 cm caneasily be accomodated, allowing storage of monomode fibres.

In FIG. 2b a single means 13 provides reservoirs for encapsulant for allof the cables simultaneously. Such means may be an integrally mouldedpart of the base.

A termination system is provided to aid branching of fibres or groups offibres from the incoming cable to respective trays. The terminationsystem illustrated comprises a series of tubes into which fibres can befed running from the base to respective trays. The tubes may be held ingroups (of say four) on a part of the base by a clip as shown.

The bases of FIGS. 2a and 2b may be used in in-line splice cases.

FIG. 3 shows an underneath view of the bases shown in FIG. 2. Electricalconnections are shown to the sets of contacts 14 and 15. The connectionsare made such that selective cutting of them can result in any of thefollowing: all cable central conductors and shields connected to thesame point (or points); central conductors plus shields of respectivecables to different points 3; and all central conductors to one point,and all shields to another point.

FIG. 4 shows a design of carrier 7 made from sheet material.

An alternative technique from that of FIG. 1 of sealing the cables attheir points of entry is shown in FIG. 5. A series of branch-off clips16 is used in conjunction with a junction box 17 to deform the outlet 3to conform to the cables 18. The junction box is positioned within theoutlet 3 and the cables pass between the box and the outlet. Thebranch-off clips cause the outlet to be deformed around the cables intoproximity with the box. The outlet is again preferbly heat-shrinkable.FIG. 5 shows a further preferred feature which may be used in any of theembodiments; the outlet 3 is shrinkable by self-contained heating means,particularly by an electrical heater which is shown powered viaconductors 19. Also shown is a band which joins together base and domeportions of the splice case. This band, which may also be electricallyheat-shrinkable, is provided with self-contained cutting means forre-entry into the splice case. A disadvantage of the use of one outlet 3which is subdivided is that all cables are preferably installed in thatoutlet before recovery can be used to seal any of them. The independentoutlets illustrated in FIG. 1 allow independent sealing of each cable,and therefore an initial partial installation, followed by addition offurther cables at a later date. The embodiment of FIG. 5 could, however,be modified to allow for this by the use of blank plugs.

FIGS. 6 and 7 show alternative ways of using one large outlet to sealseveral cables. In FIG. 6 a four legged branch-off clip or clips 16 isused, and in FIG. 7 a flexible seal 20 (such as that disclosed in GB2124439) is used around the cables to change their combined re-entrantcross-sectional shape into a circular shape compatible with the circularshape of the outlet 3. As before, the outlets 3 are preferablyheat-shrinkable, especially by electrical power.

The base and the hollow cover may be attached together as follows.

An O-ring may be used to provide a seal between the two parts which aremechanically held together by a circular clamp. Alternatively, one mayuse a band of heat-shrinkable material (as shown in FIG. 5) around thejoin line between the base and the cover. The band is preferablyshrinkable by electrical power. Electrical heat-shrinkability here isconveniently used in conjunction with electrically shrinkable outlets.

Discrete electrically shrinkable outlets may be used, shrunk intoengagement with the cables and projections on the base. The outlets inthis case may be pre-shrunk onto such projections, leaving onlyshrinkage onto the cables to be performed in the field. Alternatively,the entire installation of the outlets could be performed in the field.

FIG. 8 illustrates a preferred design of electrically shrinkableoutlets, which is most applicable to discrete outlets. The materialconstituting the tubes 3 comprises a laminate of a recoverableconductive polymer composition 21 sandwiched between two perforatedelectrodes, shown dotted in FIG. 8a. The electrodes are perforated toallow them to collapse as the outlet shrinks. Each electrode is coveredwith a layer of insulation. In the embodiment illustrated, the tubularoutlets 3 are formed from sheet material by bringing together opposingedges and clamping or bonding them at region 22. At the end regions,opposite layers of insulation 23a and 23b are removed to exposed the twoelectrodes. We prefer that the electrical heating provided by theconductive polymer composition is self-regulating, and therefore apolymer exhibiting a positive temperature coefficient of resistance(PTC) is preferably used. In order to improve the electrical performanceof the system electrical contact to the electrodes is preferably madevia a resistance material of constant-wattage behaviour. This isachieved by providing a tape 24 of zero temperature coefficient ofresistance (ZTC) as illustrated. The power is supplied via conductors19. When electrical power is applied current flows through the thicknessof the material 21, causing it to become hot and thus to shrink. In theoutlet illustrated the heater and the heat-shrinkable material are oneand the same; it is possible however to provide a discrete heater inthermal contact with a heat-recoverable outlet. The outlet shown isprovided with an internal layer of a sealing material (showncross-hatched). The sealing material is preferably heat-activatable, andwe prefer a hot-melt adhesive.

The outlet shown in FIG. 8b is stepped to accomodate the different sizesbetween the projection on the base and the cables it will carry.

FIG. 9 shows in part rectangular trays 6 which may constitute an opticalfibre organizer. Two fibre paths are illustrated. In FIG. 9a a bundle offibres 25 is shown entering the tray along one long edge and leavingalong an opposite long edge. The fibres follow a generally oval path onthe tray, one end of the oval being shown at 26 where the paths ofseveral fibres or several turns of the same fibre are illustrated. InFIG. 9b the fibre bundles 27 leave and enter along the same long edge.The arrangement of FIG. 9a is preferred.

A design of a novel tray 5 (which may also be used in an in-line splicecase) is shown in FIG. 10a in perspective view, and in FIG. 10b in planview. The tray has a central first portion with retaining means in theform of a partial rim 10, and edge second portions 28 for storingsplices 29 between fibres which are looped 26 on the tray between therims 10. The portions 28 are preferably stepped below the general levelof the tray in order to accomodate splices 29 which may include a smalltube or other protective means of diameter greater than the fibre. Thisphysical separation of the splices and the fibre loops simplifiesinstallation and ease.

The dimension W should be at least equal to the minimum storage benddiameter of the fibre. This ensures that the fibre always follows a pathof at least that diameter since the splice is accomodated on a widerportion of the tray. Each side of the tray shown may be designed forthree splice holders (shown in FIG. 11, but omitted from FIG. 10) of atype that will accept two splices. Thus, the tray will accept twelvesplices, and we prefer that a splice case can hold at least eight trays,making a total of 96 splices.

An advantage of the design of FIG. 10, over that of FIG. 1 is that theratio between straight sections of fibre to bends is larger, and thisallows greater storage. Also, the bend radius of the fibre does notdepend on the location of the splice on the tray nor on the amount offibre slack. Assymetric fibre lengths either side of the splice can bestored with easily.

The splice holder can be positioned as desired along the portions 28 andthe number of splice holders that can be accepted will of course dependon their size. FIG. 11 shows a type of splice holder 30 that can acceptvarious different types of splices. The splice holder 30 may be integralwith the tray, or it may be separate and attachable thereto by anysuitable means, for example it may be an interference fit therein. Insome circumstances it may simply rest on the tray. FIG. 11a shows asplice holder 30 with an insert 31, allowing positioning of two splicescomprising a dumb-bell shaped splice tube within which the ends of thetwo splice fibres are held (such a tube 29 is shown in FIG. 10b).Removal of the insert 31, as in FIGS. 11b, allows other types of spliceto be held.

FIGS. 12-14 disclose preferred embodiments of the invention.

FIG. 12 shows a splice enclosure for a butt splice, particularly betweenfibre optic cables. A base 32 is attached to a dome-shaped, or othercover 33 by means of a clamp or other device 34. Cables 35 can be seento enter the enclosure through the base 32. The cables may contain manyoptical fibres, groups of which may be provided within protective tubes36, or tape wrapped or twisted together etc. The fibres are then fedonto trays 37 where fibres of one cable 35 may be spliced to fibres ofthe other cable 35 (or to other fibers of the same cable). Some fibresmay pass directly from one cable to the other where, for example, abranch splice is made at an intermediate point along a single cable. Thecables 35 may include strength members 38 which may be secured directlyor indirectly to the base 32.

If desired the trays may be attached to a carrier 39 which is in turndetachably attached to the base 32 by means of screw threads or othermeans 40, for example quick-release means.

The base 32 may be sealed to the cables by any suitable means 41,thereby providing together with the dome 33 a sealed enclosure aroundthe trays and therefore around the splices in the conductors of thecable.

Means 41 preferably comprises a sealing material, for example anadhesive, mastic or gel block through which the cables 35 pass. Thesealing material may be surrounded by a sleeve or other cover means 42.Such a sleeve 42 may be of the wrap-around design, opposing longitudinaledges thereof being held together by a channel or other means 43.

The enclosure can be removed substantially (and preferably entirely)from the splice as follows. Firstly, the means 41 is removed, forexample aided by heating to soften any adhesive or other sealingmaterial present. The clamp 34 and dome 33 may be removed from the base.The screws 40, or other means, are then undone and the base can be slid(vertically upwards as drawn) over the trays 37 and away from thespliced cables. The means 40 are preferably enclosed by the cover whenattached to the base. The base can be seen to have a central hole largerenough to accept the trays 37. The carrier 39 may then be removed. Itmay have a split periphery allowing it to be removed laterally from thecables. Such a split periphery can be seen not to be disadvantageoussince the carrier 39 lies wholly within the (preferably tubular) base,and therefore there is no split against which the sleeve 42 or dome 33must seal. The carrier may therefore comprise two or more disengageableparts. It will be understood, therefore, that the base is preferablytubular and does not therefore have a peripheral split. In the absenceof such a split, it will have to have a central (i.e. not breaking ontoan edge) hole through which the trays can pass.

The enclosure can thus be dismantled and removed from the splice withoutdisturbing the splices and lengths of fibre organized on the trays 37.If desired, of course the trays can also be removed. This can be donewithout signals carried out by the fibre being disturbed.

The various components of a preferred enclosure are shown in FIG. 13.Here the trays 37 can be seen in more detail hinged to a carrier 39 byhinges 44 which are preferably arranged in stepped fashion. A means 45is visible for organizing fibres such that they do not follow a bend oftighter radius than their so-called minimum bend radius, commonly 37.5mm. Such means 45 may comprise a substantially cylindrical projectionfrom the base of the tray. Means 46 may be provided for holdingindividual fibre splices. Means 46 may comprise grooves, preferablyaligned obliquely (say 45°) relative to the length of the trays.

Means 41 for sealing between the base and the cables is also shown inmore detail. It preferably comprises a block of sealing material havinglaterally open channels 49 into which cables may be positioned. Theblock is then surrounded by heat-shrinkable sleeve 42, which overlapsthe base 72. The sleeve is preferably electrically heat-shrinkable andpreferably of wrap-around design and may be powered through busses 48that extend along (or provide) opposed longitudinal closure rails 47that may be held together by a closure channel or other means (43 inFIG. 12).

For improved sealing, or ease of installation or re-entry, the block 41may be electrically-heatable, for example through power leads 50.

A preferred tray is shown in further detail in FIG. 14. The tray mayhave means 51, such a rim, optionally with extending tabs, that help tokeep coiled fibre within the tray. Such means 51 may be provided inconjunction with means 52, such as indents, in the cylinder 45 such thatfibre can be positioned around the cylinder but is unlikely accidentallyto be removed. A cover or other means 53 is provided to preventindividual fibre splices from leaving the holder 46. The tray has anopening 54 through which fibres, or a bundles of fibres can enter.

In the design illustrated the amount of dead fibre required on the traysmay be much less, say 20%, than on prior art designs. The dead lengthis, in general, the minimum length of fibre needed to install a spliceprotection anywhere on the splice holder, and is typically about 1meter. The splice holders may be positioned on a special way on thetray, so that the fibres may be stored under the splice holder. This mayresult in a reduced number of loops of the fibres, and threfore a lowerattenuation which is useful for long distance runs of fibres.

The ability for the enclosure to be removed whilst signals are stillpassing along the fibres make re-entry, repair an modifications to theenclosure of splice much simplier and cheaper. For example cablereplacement or addition is simplified.

The oblique orientation of the splice holder 46 allows longer spliceprotection sleeves to be accomodated. Also, more splices can beaccommodated than on many prior art designs.

For the avoidance of doubt it is noted that the invention provides adesign of cable splice enclosure that can be substantially entirelyremoved from the splice without excessively interrupting signalstransmitting by the conductors of the cable. Any one or more of thedesign features disclosed above may be chosen, and such features may beused in conjunction with any one or more of the features disclosed aboveas part of EP0159857 (Raychem).

We claim:
 1. An enclosure capable of enclosing a butt splice between atleast two optical fibre cables, which comprises:a base having outletsthrough which respective cables can pass; at least one optical fibreorganizer capable of storing a optical fibre in a path from one of theoutlets to another of the outlets, said path having a minimum radius ofcurvature no smaller than the minimum bend radius of said optical fibre;and a hollow cover capable of surrounding the organizer and when thecover is fixed to the base to close the enclosure; the base beingremovable from the splice by sliding over the organizer.
 2. An enclosureaccording to claim 1, in which at least two outlets are formed at thebase from subdivision of a single tubular member.
 3. An enclosureaccording to claim 1, which additionally comprises means for forming aseal between the base and the cables.
 4. An enclosure according to claim2, in which the outlets are formed in a sealing material the sealingmaterial being surrounded by a heat-shrinkable sleeve.
 5. An enclosureaccording to claim 4, in which the sleeve comprises a conductivepolymeric material that exhibits positive temperature coefficient ofresistance behaviour.
 6. An enclosure according to claim 1, in which thebase has means for providing a reservoir for an encapsulant around acable.
 7. An enclosure according to claim 1, in which the optical fibreorganizer comprises one or more optical fibre trays.
 8. An enclosureaccording to claim 7, in which the trays are each hinged to a carrier,the hinge line running substantially perpendicular to the cables passingthrough the base.
 9. An enclosure according to claim 7, in which thetrays comprise a first portion which can accept a loop of optical fibreand a second portion which can accept an optical fibre splice.
 10. Anenclosure according to claim 9, in which the first portion has means forlocating the loop adjacent an edge of the tray, and the second portionlies intermediate opposing edges of the tray.
 11. An enclosure accordingto claim 1, in which the trays are attached to a carrier, which carrieris detachably attached to the base.
 12. An enclosure according to claim11, in which the detachable attachment is by means of a screw-thread.13. An enclosure according to claim 11, in which the detachableattachment is by means of a quick-release device.
 14. An enclosureaccording to claim 11, in which the detachable attachment is enclosed bythe cover when attached to the base.
 15. An enclosure capable ofenclosing a butt splice between cables which comprises a base throughwhich respective cables can pass;at least one organizer capable ofstoring splices between conductors of the cable; and a hollow covercapable of surrounding the organizer when the cover is fixed to the baseto close the enclosure;the base being removable from the splice withoutsevering the spliced conductors.